1. Field of the Invention
The present invention relates to an encoding apparatus for performing a bit rate reduction coding of a video signal to compress its information for recording and transmission.
2. Description of the Prior Art
Such a video signal encoder is known that eliminates redundancy of information in time domain by motion compensation. A prediction process in the motion compensation is executed on a frame-by-frame or field-by-field basis. Such video signal encoder is shown in CCITT Recommendation H.261, "VIDEO CODER FOR AUDIOVISUAL SERVICES AT px64 kbit/s" (approved on December 1990).
The existing television systems employ the known interlaced scanning method for scanning every alternate lines in a TV picture, whereby each frame has time and spatial delays. Hence, when the TV picture is not a completely still image, the redundancy can hardly be reduced by the conventional interframe prediction technique.
On the other hand, the field-by-field prediction may be considered to process each field (not frame) of the TV signal by prediction from data of the preceding field. The advantage of this process is that the time distance between fields is half that between frames. However, the prediction signal tends to be out-of-phase from the scanning of data of a block to be encoded and will thus be declined in accuracy.